Just days after the Belgian passed a medical as part of his transfer from Arsenal, the defender is struggling with a muscular problem.
The Belgium international passed a medical over the weekend before completing his 19 million euro transfer from Arsenal, but the Catalans have revealed that the 28-year-old's debut will be delayed following his World Cup exploits.
Vermaelen made two appearances for Marc Wilmots' men at this summer's tournament in Brazil, where Belgium made it to the quarterfinals.
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"The first-team player Thomas Vermaelen has a hamstring injury in his right leg that he sustained in June during the World Cup," a statement on the club's official website reads. "The player will undergo physiotherapy. His return to regular training action depends on the evolution of the injury."
Vermaelen signed a contract with Barcelona until the summer of 2019 on Sunday.
The Camp Nou side previously secured the services of Marc-Andre ter Stegen, Claudio Bravo, Jeremy Mathieu, Alen Halilovic, Ivan Rakitic and Luis Suarez.